Abstract

The first observation of the concurrent production of two J/ψ mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead (pPb) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of 174.6 nb−1. The two J/ψ mesons are reconstructed in their μ+μ− decay channels with transverse momenta pT>6.5 GeV and rapidity |y|<2.4. Events where one of the J/ψ mesons is reconstructed in the dielectron channel are also considered in the search. The pPb→J/ψJ/ψ+X process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is σ(pPb→J/ψJ/ψ+X)=22.0±8.9(stat)±1.5(syst) nb. A fit of the data to the expected rapidity separation for pairs of J/ψ mesons produced in single (SPS) and double (DPS) parton scatterings yields σSPSpPb→J/ψJ/ψ+X=16.5±10.8(stat)±0.1(syst) nb and σDPSpPb→J/ψJ/ψ+X=5.4±6.2(stat)±0.4(syst) nb, respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of σeff>1.0 mb at 95% confidence level. © 2024 CERN, for the CMS Collaboration 2024 CERN